1. Field of the Invention
This invention relates to the field of semiconductor manufacturing and, in particular, to an off center three point carrier for wet processing semiconductor substrates.
2. Description of the Related Art
Semiconductor wafer carriers, also referred to as semiconductor wafer cassettes, are known in the art. Such carriers are typically utilized for storage, transportation and processing of semiconductor substrates used in the fabrication of semiconductor devices. A typical example of such a semiconductor substrate is a semiconductor wafer. For purposes of illustration only, a semiconductor wafer will be used as the semiconductor substrate. The semiconductor wafer carriers are configured to carry a plurality of semiconductor wafers. In particular, the semiconductor wafer carriers usually include a plurality of slots configured to receive a single semiconductor wafer.
Typically, the semiconductor wafers are arranged within the wafer carrier outside of a semiconductor processor. The wafer carrier is thereafter transported, with the wafers inside, into the processing apparatus, for example, an etching bath, which are typically configured to process the wafers within the carrier.
FIGS. 1 and 2 illustrate a conventional three point wafer carrier 10 used in the processing of semiconductor wafers W. The carrier 10 includes first and second side rails 12, 14 and a bottom rail 16. The first and second side rails 12, 14, are positioned in a spaced parallel relation by U-shaped or V-shaped supports 20. The bottom rail 16 is positioned on the supports 20 at a point that is equidistant between the two side rails 12, 14 at the lowest and most centralized position of the supports 20. The three rails 12, 14, 16 define a wafer receiving portion 30 where the wafers W are to be placed. Each of the rails 12, 14, 16 are provided with a series of equally spaced slots 18, sized and aligned to support a plurality of wafers W in a spaced, parallel relation. The series of slots 18 extend to the ends of the rails 12, 14, 16. Accordingly, wafers W placed within the slots 18 have three points of contact with the carrier 10.
Typically, the supports 20 are made out of a flexible material, such as TEFLON (synthetic resinous fluorine). The carrier 10 is designed such that when wafers W are placed within the carrier 10, the weight of the wafers W applied onto the bottom rail 16 causes the supports 20 to move in the direction illustrated by the arrow A. As the supports 20 move, the first and second side rails 12, 14 also move (the original positions of the rails 12, 14 are illustrated in phantom as reference numerals 12a, 14a) producing a tension proportional to the total weight of all of the wafers W within the carrier 10. The tension maintains the wafers W in place within the carrier 10. The carrier 10 is placed into a semiconductor processor where, for example, etching of the wafers W occurs.
Although the conventional carrier 10 works well, it has a few shortcomings. For example, during wet etching of the wafers W, the etchant material has a tendency to gravitate in the slots 18 of the bottom rail 16. Thus, even after removing the carrier 10 from the semiconductor processor, etchant is still in contact with the wafers W. This condition can cause the etching of the wafer W to continue. There will be poor etching and drying in these areas. In addition, the wafers W may also become stained at these areas. Portions of the etched wafers W at these areas may become unusable. Therefore, there is a need and desire to prevent wet etchant or acids from collecting within the rails of a three point wafer carrier to ensure the proper etching and drying of semiconductor wafers.